The work on the structure of catalase is progressing well and is almost certainly going to take a significant proportion of the research effort during the next 12 months. It is possible that a high-resolution structure determination will be achieved during this time. It is anticipated that the refinement of our various lactate dehydrogenase (LDH) structures will progress more rapidly with the probable completion of the dogfish M4, pig M4 and pig H4 amino acid sequences. The high-resolution structure of the testicular mouse LDH isozyme is also confidently expected. Further studies on glyceraldehyde-3-phosphate dehydrogenase substrate and analogue derivatives should clarify the nature of the catalytic mechanism in this enzyme. A study of a different crystal form of an apo-enzyme has been initiated and should eventually show conformational changes which occur during binding of coenzyme. A good deal of progress is expected in the analysis of protein folding and structural relationships for which ground work has now been laid. This should elucidate some architectural principles common to all protein structures. BIBLIOGRAPHIC REFERENCES: Eventoff, W., L. Hackert, S.J. Steindel, M.G. Rossmann. 1975. A structural comparison of porcine B4 and dogfish A4 isozymes of lactate dehydrogenase. In Isozymes. I. Molecular Structure. Markert, C.L., ed. Academic Press, New York. pp. 137-150. Argos, P., C. Ford, M.G. Rossman. 1975. An application of the molecular replacement technique in direct space to a known protein structure. Acta Crystallogr. A31:499-506.